Solo battleships already dominate L4 missions. Doing them with an additional damage dealer is easy/speed mode. Efficiency goes down from there. Three ships is overkill already and by doing it with 6 ships you are wasting time.
Split your single fleet into two separate ones and do 2 missions at once.
EDIT: Oh and on top of that the local player pirate crowd will be pleased to have you as a new toy once they realize what you are doing.
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